This invention relates to an induction system for an internal combustion engine and more particularly to an improved induction system that insures better low speed, low temperature running characteristics.
It is well known that it is desirable to promote a high degree of turbulence in the combustion chamber of an internal combustion engine immediately prior to ignition. Such turbulence has the effect of increasing flame propagation speed and, therefore, improving the smoothness and efficiency of the running of the engine. Arrangements have been proposed for increasing turbulence such as the use of shrouded intake ports for generating a swirl during induction or the use of large squish areas which promotes turbulence during the compression stroke. Each arrangement, however, has well known disadvantages. The use of shrouded ports has a tendency to significantly reduce the volumetric efficiency of the engine at high loads. The use of large squish areas, on the other hand, has the effect of increasing the emission of certain unwanted exhaust gas constituents, particularly unburned hydrocarbons.
To overcome the aforenoted defects it has been proposed to provide with an engine, in addition to the conventional main induction passage a relatively small subinduction passage through which the intake charge is delivered during light load and low speed running. This arrangement has the advantageous effect of not reducing volumetric efficiency and further increasing fuel economy and smoothness in engine running at low speeds as well as showing a significant improvement in low speed fuel economy. Several embodiments of engines of this type may be found in my application for United States Letters Patent entitled Control of Carburetor Supplied Induction System, Ser. No. 838,353, filed Sept. 30, 1977 and assigned to the assignee of this invention.
One reason why conventional intake systems provide poor low speed, low temperature running characteristics is the likelihood of fuel condensation on the inner surfaces of the induction passages. Such condensation results from the low velocities at which the charge passes through the induction passages during idle and low speed operation and from the temperature effects of the induction system, when the engine is cold. To overcome these effects, it has been common practice to run the engine richer than normal during low speed and low temperature operation. Obviously this has the effect of decreasing fuel economy and increasing the emission of unwanted exhaust gas constituents such as unburned hydrocarbons and carbon monoxide. The arrangement shown in my aforenoted United States patent application Ser. No. 838,353 reduces these effects by permitting operation at normal fuel air ratios even though the temperature is low and the engine speed is low. Even through the structure shown in that application is particularly useful in this regard, it has been found that is some circumstances the abrupt rate of change in flow through the various induction passages still causes some deviation in the air fuel ratio from that desired.
It is, therefore, a principal object of this invention to provide an improved induction system for low speed and low temperature operation.
It is another object of the invention to provide an induction system for an internal combustion engine that offers efficient induction and combustion under all operating conditions.